NM doesn't detect actual offline status with just a floating bridge right away (only after some timeout)
In Fedora 29's NetworkManager-1.12.4-2.fc29.x86_64, I noticed a peculiar behaviour I don't remember from earlier versions of NM: when you resume a laptop with active libvirt's bridge (virbr0) but no other device, it thinks for few minutes that the computer is online:
[root@cihla ~]# ip -6 r ; ip -4 r ; nmcli c s --active ; nmcli g
::1 dev lo proto kernel metric 256 pref medium
fe80::/64 dev tap0 proto kernel metric 256 pref medium
192.168.124.0/24 dev virbr0 proto kernel scope link src 192.168.124.1 linkdown
NAME UUID TYPE DEVICE
virbr0 efa53a4b-b1a5-4479-b99b-781001fb6085 bridge virbr0
STATE CONNECTIVITY WIFI-HW WIFI WWAN-HW WWAN
connected full enabled enabled enabled enabled
This is clearly wrong, the status should never be connected
/full
when there's no default route…
After some timeout (2, 3, 5 minutes? I don't remember), NM notices and things depending on NM connection status continue working normally.